Exploration is carried out by aircore drilling, a low cost, rapid and accurate drilling method for unconsolidated sand units. The most prospective area is located around Dinner Hill in the northwest of the tenements, Figure 2. Here fresh greensands occur at shallow depth along the western margin of the Dandaragan Trough over an area of 60 square kilometres. Within 20 square kilometres of the Dinner Hill prospect JORC compliant resources for both phosphate and the K-Max process, have been estimated. Thick intersections of phosphate and glauconite have also been drilled at the Dambadjie prospect about 60km to the south of Dinner Hill.
Figure 2: Dinner Hill location
The Dandaragan Trough is part of the much larger Perth Basin a deep linear sedimentary basin which extends for over 1000km in the southwest of Western Australia from the south coast to north of Geraldton. The total extent of the Dandaragan Trough is over 500km but it is only in the region known as the Dandaragan Plateau where greensand is found close to surface and amenable to exploitation. Greensand refers to a lithology that is a mixture of green coloured glauconite and silica sand, Figure 3. They tend to be soft, friable units that weather readily at surface leaving laterite and sandy soils.
Figure 3: Greensand
Greensand was deposited in shallow, protected marine basins some 60 million years ago in the Cretaceous Period. Potash West’s tenements overlay three greensand formations and a chalk unit which collectively are known as the Coolyena Group. The most commercially important units are the Poison Hill Greensand and Molecap Greensand which are usually separated by the Gingin Chalk. Figure 4 shows drill samples through the formations which typically return sandy, reddish, cover sediments and windblown sand near the top of the hole. The top of the Poison Hill Greensand is usually oxidised and presents as red brown sandy clay becoming green near the base of oxidation. Here the potash content increases to 2-3% and phosphate nodules are common and may contain 10-15% P2O5. The base of the Poison Hill is marked by the appearance of a thin chalk unit below which is the Molecap Greensand. Dark green in colour it contains potash grades averaging 4.5% and is the target for the K-Max process. Phosphate nodules are found in all three lithologies but the most encouraging grades and metallurgical properties are in the Dinner Hill area.
Figure 4: Drillhole samples
At Dinner Hill the Company has undertaken extensive aircore drilling resulting in the delineation of both phosphate and potash resources as well as a large exploration target, Dinner Hill Extended, Figure 5. Both phosphate and potash mineralisation remains open to the north east and south. To the north there is some 4km of untested strike where phosphate grades appear to be increasing in an area of basin closure. The Dinner Hill Phosphate Deposit contains an Indicated Mineral Resource of 250Mt at 2.9% P2O5, 3.6% K2O, and 4.5% CaO. The northern most section, Figure 6, shows the distribution of the phosphate mineralisation and the typically higher grades in the north of the resource.
Dinner Hill Indicated Phosphate Resources by Cut-off Grade
|Lower Cut-off Grade (% P2O5)||Tonnes||Grade
Figure 5: Dinner Hill resource areas
Figure 6: Dinner Hill phosphate resource, section 6,638,400mN
The Dinner Hill Potash Deposit, suitable for processing by the K-Max process, is estimated to contain 195 Mt at 3.8% K2O (potash) and 1.6% P2O5 (phosphate). Figure 7 shows a typical section through the potash resource illustrating the location of higher grades the Molecap Greensand.
Dinner Hill Deposit Resource Summary
|Unit Category||Tonnes (Mt)||K2O (%)||P2O5 (%)|
|Poison Hill Greensand||Indicated||121||1.5||1.4|
Figure 7: Cross section through the Dinner Hill K-Max resource